Jökulhlaups

Icebergs were left perched on dry land after a jökulhlaup drained Iceberg Lake (Wrangell-St. Elias National Park, Alaska)

NPS Photo

Jökulhlaups (an Icelandic word pronounced yo-KOOL-lahp) are glacial outburst floods. They occur when a lake fed by glacial meltwater breaches its dam and drains catastrophically. These lakes can take a number of forms:

• Ice dammed lakes that are held in by the glacier ice itself
• Moraine, rock, or sediment dammed lakes
• Lakes that lie form beneath glaciers

In order for a jökulhlaup to occur, the lake water levels must reach a critical point such that the lake:

• Causes its ice dam to float
• Overtops its dam, causing rapid incision into the sediment, rock, or ice that contains it
• Carves large meltwater channels beneath the glacier ice that allow for rapid drainage

Jökulhlaups may occur with a somewhat regular periodicity, but others drain without warning. 

To learn more about glaciers, glacier features, and glacial landforms, see the Glaciers & Glacial Landforms Page.

Related Links

• NPS—Geoscience Concepts
• NPS—Geologic Tour
• NPS—Geodiversity Atlas
• NPS—Geology